You should be able to use an IF statement like:
<?php
if ($eCart1->ConditionalTotal("Quantity", "eCartCatID", "1")) {
echo "#fldsetcs { display:block; }";
}
?>
The ConditionalTotal function will return the sum of the first column where the second column equals the third value. So the if statement above will be the Total Quantity where eCartCatID equals 1.